Chrometanning

Chrometanning, commonly referred to as chrome tanning, is a method of tanning hides using chromium salts, principally chromium(III) salts such as basic chromium sulfate. In this process, chromium ions form cross-links with collagen fibers in the hide, converting it into stable, flexible leather that resists heat, enzymes, and water. Chrome-tanned leather is typically softer and more uniform and can be produced much faster than vegetable-tanned leather.

Chrome tanning was developed in the 19th century and became the dominant tanning method in the 20th century due to speed, consistency, and the ability to process a wide range of hides. It enabled mass production of leather products with reproducible properties.

The process generally involves preparing the hide, followed by immersion in a chromium tanning liquor. After tanning, the leather is neutralized, retanned, dyed, fatliquored, and finished. The chromium binds to the collagen to form durable cross-links, allowing the leather to be produced in as little as a day or two.

Environmental and health considerations focus on the management of chromium in wastewater and the possibility of chromium(VI) formation under certain conditions. Modern tanneries control pH, temperature, and oxidation to minimize Cr(VI) formation and employ wastewater treatment to recover chromium and reduce emissions.

Chrome-tanned leather is widely used in footwear, upholstery, and automotive interiors; retanning and finishing techniques tailor properties for specific applications. Alternatives include vegetable, aldehyde, and synthetic tanning methods.